Lawyers are due to launch a legal challenge today on behalf of four women held at Yarl's Wood detention centre, claiming their incarceration amounts to "cruel, inhumane and degrading" treatment that breaches their human rights.

The lawyers, who say they will submit the application at the high court in London, are applying for a judicial review of the government's detention policy, claiming it breaches articles 3, 5 and 8 of the European convention on human rights.

"This disgraceful policy will now be the subject of legal challenge," said Phil Shiner, of Public Interest Lawyers, which is bringing the action. "It is unlawful and we are calling, on behalf of our clients, for the policy to be struck down and for there to be an independent investigation."

Serco, the private company that runs Yarl's Wood, has described allegations of inhumane and degrading treatment as "unfounded and untrue".

The move comes amid an increasingly bitter row over the treatment of the women and children held at the Bedfordshire detention centre. Home Office minister Meg Hillier sent a letter to MPs last week denying claims by women at Yarl's Wood that they have been on hunger strike for three weeks. Hillier said that, although there are "a small number of detainees … refusing formal meals from the canteen, they are buying food from the centre's shop and vending machines and having food delivered by visitors".

In her letter, Hillier said the women's health had been checked and there was no cause for concern. She also denied claims by detainees that they had been racially abused and assaulted during a protest last month. She said: "All the detainees are treated with dignity and respect ... I can assure you that there was no such behaviour by our staff."

However, detainees, campaigners and some MPs have reacted angrily to her letter. On Friday, 34 women at Yarl's Wood issued a statement through the Black Women's Rape Action Project insisting they were still on hunger strike. The strike enters its fourth week today.

"At no particular point in time have we gone to eat in the dining room, got food from the vending machines or at the shop," the women's statement said.

They also stand by their claims that some of them were assaulted during the protest on 8 February and that others were called "black monkeys".

Cristel Amiss, speaking on behalf of the women's project, said: "The government is falling on its face with its vain attempts to smear hunger strikers. We are in daily contact with hunger strikers and know that vacuous claims that women are treated with dignity and respect mean nothing in the face of overwhelming evidence of appalling conditions and abuse."

Evan Harris, a Liberal Democrat MP, criticised the government's reaction to the protest and said he had written to the chief inspector of prisons asking her to conduct an "urgent unannounced visit" to investigate the situation.

John McDonnell, a Labour MP, has tabled an early day motion calling for an independent inquiry into the recent allegations of "violence, mistreatment and racist abuse" at the centre.

"There are real concerns," he said, "and all we are asking the government to do is to look at these seriously and hold an independent inquiry. Instead, by turning a blind eye they are simply exacerbating the problems and this can lead to more serious problems like riots and the burning down of detention centres."

"We have proof that 'food refusers' are regularly purchasing food from the shop and vending machines, and that they have all been seen by doctors who have no concerns about their health," she said.

Today's legal challenge follows a report by the children's commissioner last month that said children held at the centre faced "extremely distressing" arrest and transportation procedures and were subjected to prolonged and sometimes repeated periods of detention.

Shiner said the application for a judicial review was based on the cases of four women and three children. He said he would be asking for a judge to look at the case within 24 hours and hoped a hearing would start within a month.